This project is a study of DNA polymorphisms related to the genetic defect of cystic fibrosis (CF) and their segregation in a highly inbred population. The long-term objective of this project is to identify gene sequences specifically related to the basic genetic defect responsible for CF, and ultimately to identify and characterize the CF gene. The gene sequences originally identified may represent the actual altered (i.e. "CF") gene, but are more likely to be linked DNA sequences (marker sequences). Gene sequences that segregate with the CF phenotype will be identified by linkage analysis of restriction fragment length polymorphisms primarily in a large kindred containing multiple CF affected individuals. The kindred is part of a well-defined inbred population, the Ohio Old Order Amish. The search for linked sequences must have an arbitrary beginning in the absence of a chromosomal assignment for the CF gene. The first probes tested for linkage to CF have been localized to chromosome 6 and to the short arm of chromosome 11. These chromosomes have abundant DNA and protein markers clustered into linkage groups, which will allow rapid progress in construction of linkage or exclusion maps for CF. A flow-sorted library will be constructed for chromosome 9. Cloned probes from this library will be assigned to a subregion of a 9 using mutant cell lines. These probes will be used for linkage analysis in the informative CF families. An additional goal of this research is to describe a relationship between inbreeding and neutral DNA drift, by studying the distribution and frequency of DNA polymorphisms in an inbred population.